This application claims priority to Canadian Patent Application No. 2,381,214 filed Apr. 10, 2002.
This invention relates to heat exchangers, and in particular, to heat exchangers involving gas/liquid, two-phase flow, such as in evaporators or condensers.
In heat exchangers involving two-phase, gas/liquid fluids, flow distribution inside the heat exchanger is a major problem. When the two-phase flow passes through multiple channels which are all connected to common inlet and outlet manifolds, the gas and liquid have a tendency to flow through different channels at different rates due to the differential momentum and the changes in flow direction inside the heat exchanger. This causes uneven flow distribution for both the gas and the liquid, and this in turn directly affects the heat transfer performance, especially in the area close to the outlet where the liquid mass proportion is usually quite low. Any maldistribution of the liquid results in dry-out zones or hot zones. Also, if the liquid-rich areas or channels cannot evaporate all of the liquid, some of the liquid can exit from the heat exchanger. This often has deleterious effects on the system in which the heat exchanger is used. For example, in a refrigerant evaporator system, liquid exiting from the evaporator causes the flow control or expansion valve to close reducing the refrigerant mass flow. This reduces the total heat transfer of the evaporator.
In conventional designs for evaporators and condensers, the two-phase flow enters the inlet manifold in a direction usually perpendicular to the main heat transfer channels. Because the gas has much lower momentum, it is easier for it to change direction and pass through the first few channels, but the liquid tends to keep travelling to the end of the manifold due to its higher momentum. As a result, the last few channels usually have much higher liquid flow rates and lower gas flow rates than the first one. Several methods have been tried in the past to even out the flow distribution in evaporators. One of these is the use of an apertured inlet manifold as shown in U.S. Pat. No. 3,976,128 issued to Patel et al. Another approach is to divide the evaporator up into zones or smaller groupings of the flow channels connected together in series, such as is shown in U.S. Pat. No. 4,274,482 issued to Noriaki Sonoda. While these approaches tend to help a bit, the flow distribution is still not ideal and inefficient hot zones still result.
In the present invention, a flow augmentation device that includes a turbulizing structure about a core pipe is located in a heat exchanger manifold to distribute liquid phase fluid through a plurality of tube members connected to the manifold. The turbulizer structure includes a helical fin in one preferred embodiment.
According to the present invention, there is provided a heat exchanger that includes a manifold defining an inlet manifold chamber having a manifold chamber inlet opening, a plurality of tube members each defining an internal flow channel having an opening into the manifold chamber, and an elongate core pipe fixed in the manifold chamber, the core pipe having a turbulizing structure extending along a portion thereof passing adjacent the flow channel openings for distributing liquid phase fluid flowing into the manifold chamber among the flow channels. Preferably, the turbulizing structure includes a helical fin, however in some applications different turbulizing structures could be used, such as spaced apart annular rings projecting from an outer surface of the core pipe or annular groves formed on an outer surface of the core pipe.